Regional underpressure: a factor of uncertainty in the geothermal exploration of deep carbonates, Gödöllő Region, Hungary

Abstract

Hungary has a remarkable geothermal potential, and there are ongoing projects investigating the possibilities
of thermal water utilization. The regional hydrodynamic assessment of one of the most promising geothermal sites of Hungary, the Go¨do¨ll}o Hills Region, could provide valuable additional information to them. The aim of this research was not only to carry out a regional study but also to demonstrate the relevance of the hydrodynamic approach in the reconnaissance phase of exploration. Regional evaluation was carried out based on the created database of preproduction wells’ hydraulic, temperature, and geochemical data. Based on the dataset from the depth extending to -2300 m asl, it could be shown that the temperature field (up to 120 �C) and the reservoir conditions are favorable: structurally influenced Triassic Main Dolomite and Dachstein Limestone, Miocene, and Upper Pannonian formations, and fluid flow is basically topography induced. The recharge and discharge zones of the gravity-driven system, the basement elevation, and the temperature distribution show good correlation. The vertical connections between Pannonian and Eocene-Triassic
basement reservoirs could be followed through the changes of pressure regimes and by the interaction of ‘‘fresh’’ and ‘‘basinal’’ fluids of the region. It has been revealed that, due to the differentiated uplifting of the region in the Pliocene and the Quaternary, the pore pressures in the aquitards and in the basement reservoir have been shifted toward subhydrostatic, indicating geologically transient pore pressures. The detected subhydrostatic pressure gradients cause downward vertical groundwater flow in the Hills characterized
by restricted recharge across low permeability strata. Upward vertical flow appears from the basement
carbonate reservoir toward the highest negative pressure increment values in the aquitards. The underpressure in the basement carbonate reservoir causes an uncertainty factor in the exploration of a potential geothermal site. The area was differentiated based on flow and pressure conditions for geothermal exploitation.

Full text

THEMATIC ISSUE
Regional underpressure: a factor of uncertainty in the geothermal
exploration of deep carbonates, Go
¨do
¨ll}
o Region, Hungary
Judit Ma
´dl-Sz}
onyi
1
•Eszter Pulay
1
•A
´da
´mTo
´th
1
•Petra Bodor
1
Received: 15 April 2014 / Accepted: 2 June 2015
ÓSpringer-Verlag Berlin Heidelberg 2015
Abstract Hungary has a remarkable geothermal poten-
tial, and there are ongoing projects investigating the pos-
sibilities of thermal water utilization. The regional
hydrodynamic assessment of one of the most promising
geothermal sites of Hungary, the Go
¨do
¨ll}
o Hills Region,
could provide valuable additional information to them. The
aim of this research was not only to carry out a regional
study but also to demonstrate the relevance of the hydro-
dynamic approach in the reconnaissance phase of explo-
ration. Regional evaluation was carried out based on the
created database of preproduction wells’ hydraulic, tem-
perature, and geochemical data. Based on the dataset from
the depth extending to -2300 m asl, it could be shown that
the temperature field (up to 120 °C) and the reservoir
conditions are favorable: structurally influenced Triassic
Main Dolomite and Dachstein Limestone, Miocene, and
Upper Pannonian formations, and fluid flow is basically
topography induced. The recharge and discharge zones of
the gravity-driven system, the basement elevation, and the
temperature distribution show good correlation. The ver-
tical connections between Pannonian and Eocene-Triassic
basement reservoirs could be followed through the changes
of pressure regimes and by the interaction of ‘‘fresh’’ and
‘‘basinal’’ fluids of the region. It has been revealed that, due
to the differentiated uplifting of the region in the Pliocene
and the Quaternary, the pore pressures in the aquitards and
in the basement reservoir have been shifted toward sub-
hydrostatic, indicating geologically transient pore pres-
sures. The detected subhydrostatic pressure gradients cause
downward vertical groundwater flow in the Hills charac-
terized by restricted recharge across low permeability
strata. Upward vertical flow appears from the basement
carbonate reservoir toward the highest negative pressure
increment values in the aquitards. The underpressure in the
basement carbonate reservoir causes an uncertainty factor
in the exploration of a potential geothermal site. The area
was differentiated based on flow and pressure conditions
for geothermal exploitation.
Keywords Hydrodynamic evaluation Subhydrostatic
pressure Groundwater flow Go
¨do
¨ll}
o Region Hungary
Introduction and goals
The research of regional groundwater flow distribution in
natural geothermal systems is of special importance
because moving groundwater affects the underground
temperature distribution (Domenico and Palciauskas 1973;
Smith and Chapman 1983; Bethke 1985; Rybach 1985;
Van der Kamp and Bachu 1989; Deming 2002; Anderson
2005; Saar 2011 etc.). This effect was demonstrated
besides others by regional numerical simulation of Lazear
(2006) for a 600 km
2
area in the west central Colorado,
USA. The study of Lazear displayed the regional advective
heat transport by groundwater flow and the consequent
temperature anomalies in the temperature field. These
theoretical results were transformed into the practice in the
Pannonian Basin by the T-Jam (Rman and To
´th 2011) and
Transenergy (Na
´dor et al. 2014) projects. The numerical
simulations of these projects demonstrated the trans-
boundary effect of thermal water utilization in the Western
part of the Pannonian Basin, and therefore, provided the
&Judit Ma
´dl-Sz}
onyi
madlszonyi.judit@gmail.com
1
Department of Physical and Applied Geology, Eo
¨tvo
¨s Lora
´nd
University, 1/C Pa
´zma
´ny P. stny., Budapest 1117, Hungary
123
Environ Earth Sci
DOI 10.1007/s12665-015-4608-z
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